Ninety-seven per cent of right-handed (RH) individuals develop speech and language processing in the left (dominant) hemisphere of the brain, while the "minor" hemisphere controls emotional behavior. We have speculated that a hypothetical gene, <I>RGHT</i>, functions to specify left-brain dominance resulting in developing the right-handed preference. We have been collecting blood samples and cheek swabs from specific families with the aim to genetically map the hypothesized <I>RGHT</i> gene. We have collected enough samples and the next stage is to use these samples for mapping by the sib-pair method. We have published our random recessive model in which individuals with the nonfunctional recessive allele on both homologs have a 50:50 chance of either being RH or LH. We also found interesting association of hand use preference with the clockwise vs. counterclockwise scalp hair-whorl rotation. We suggest that individuals with the right gene are RH and develop clockwise hair whorls, but individuals with the recessive allele are 50:50 in hair whorl orientation. We have previously proposed that human brain and visceral organs laterality might be controlled by the Somatic Strand-specific Imprinting and selective chromatid/strand Segregation (SSIS) model. It predicted a chromosome-specific, nonrandom WW:CC segregation phenomenon where both older "Watson" strand-containing chromatids form a homologous pair of chromosomes are delivered in mitosis to one daughter cell and the older "Crick" strand-containing chromatids are delivered to the other daughter cell. This was proposed as a mechanism for cellular differentiation to produce non-equivalent daughter cells in mitosis. We have now established the existance of such biased strand segregation phenomenon in mice cells concerning chromosome 7 segregation. Interestingly th esegregation pattern is cell type regulated so that there is directed segregatio i soem cell types but random in others. In future exaperiments we want to find the mechanism of biased strand segregation of this chromosome and also we will determine whether other chromosomes are likewise subject to cell type regulated segregation process.